U.S. patent number 7,365,217 [Application Number 11/338,999] was granted by the patent office on 2008-04-29 for oxidation process.
This patent grant is currently assigned to Lyondell Chemical Technology, L.P.. Invention is credited to Roger A. Grey.
United States Patent |
7,365,217 |
Grey |
April 29, 2008 |
Oxidation process
Abstract
A process is disclosed for reacting an olefin, hydrogen, and
oxygen in a reactor in the presence of an epoxidation catalyst
comprising a transition metal zeolite and a noble metal to produce
a product stream comprising an epoxide and an alkane. The alkane is
separated and oxidized to at least one oxygenated product.
Inventors: |
Grey; Roger A. (West Chester,
PA) |
Assignee: |
Lyondell Chemical Technology,
L.P. (Greenville, DE)
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Family
ID: |
37943855 |
Appl.
No.: |
11/338,999 |
Filed: |
January 25, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20070173655 A1 |
Jul 26, 2007 |
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Current U.S.
Class: |
549/533; 568/399;
568/403; 568/910 |
Current CPC
Class: |
B01J
23/6484 (20130101); B01J 29/89 (20130101); C07C
29/48 (20130101); C07C 29/50 (20130101); C07C
45/33 (20130101); C07D 301/04 (20130101); C07D
301/06 (20130101); C07D 301/08 (20130101); C07D
301/12 (20130101); C07C 45/33 (20130101); C07C
49/08 (20130101); C07C 29/50 (20130101); C07C
31/10 (20130101); C07C 29/50 (20130101); C07C
31/205 (20130101); C07C 29/48 (20130101); C07C
31/10 (20130101); C07C 29/48 (20130101); C07C
31/205 (20130101); B01J 2229/186 (20130101); B01J
2229/20 (20130101) |
Current International
Class: |
C07D
301/10 (20060101); C07C 29/03 (20060101); C07C
45/00 (20060101) |
Field of
Search: |
;549/533
;568/357,403,910,959,399 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1001038 |
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Jun 1989 |
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BE |
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0 126 488 |
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May 1984 |
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EP |
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0 345 856 |
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May 1989 |
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EP |
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4-352771 |
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Dec 1992 |
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JP |
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WO 03/093202 |
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Nov 2003 |
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WO |
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WO 2005/042449 |
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May 2005 |
|
WO |
|
Other References
R Szostak, Non-aluminosilicate Molecular Sieves in Molecular Sieves
Principles of Synthesis and Identification (1989) 205. cited by
other .
G. Vayssilov, Catal, Rev.--Sci. Eng. 39(3) (1997) 209. cited by
other .
S. Hsu, Hydrocarbon Process., Int. Ed, 66(4) (1987) 43. cited by
other .
B. Liao et al., Chem. Eng. J, 84 (2001) 581. cited by other .
V. Gokhale et al., Ind. Eng. Chem. Res. 34 (1995) 4413. cited by
other .
J. Labinger, J. Mol. Catal. A: Chem. 220 (2004) 27. cited by other
.
F. Cavani et al., "The Multifunctional Properties of Heterogeneous
Catalysts, Active and Selective in the Oxidation of Light
Paraffins," in Studies in Surface Science and Catalysis 110:
3.sup.rd World Congress on Oxidation Catalysis R. Grasselli et al.
Ed. (1997) 19. cited by other .
Q. Zhang et al., J. Catal. 202 (2001) 308. cited by other .
G. Suss-Fink et al., Appl. Catal. A 217 (2001) 111. cited by other
.
P. Ratnasamy et al., Stud. Surf. Sci. Catal. 97 (1995) 367. cited
by other .
P. Ingallina et al., Sci. Tech. Catal. (1994) 31. cited by other
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W. Sanderson, Pure Appl. Chem. 72 (7) (2000) 1289. cited by other
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T. Tatsumi et al., J. Chem. Soc., Chem. Commun. (1992) 1446. cited
by other.
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Primary Examiner: Dentz; Bernard
Assistant Examiner: Gallis; David E
Attorney, Agent or Firm: Han; Yuanzhang
Claims
I claim:
1. A process comprising: (a) reacting an olefin, hydrogen, and
oxygen in the presence of a buffer and an epoxidation catalyst
comprising a transition metal zeolite and a noble metal to produce
a product stream comprising an epoxide and an alkane; (b)
separating the alkane from the product stream; and (c) oxidizing
the alkane to at least one oxygenated product.
2. The process of claim 1 wherein the noble metal is supported on
the transition metal zeolite.
3. The process of claim 2 wherein the transition metal zeolite is a
titanium zeolite.
4. The process of claim 1 wherein the noble metal is supported on a
carrier.
5. The process of claim 4 wherein the carrier is selected from the
group consisting of carbon, titania, zirconia, niobia, silica,
alumina, silica-alumina, titania-silica, zirconia-silica,
niobia-silica, ion-exchange resins, and mixtures thereof.
6. The process of claim 4 wherein the transition metal zeolite is a
titanium zeolite.
7. The process of claim 1 wherein step (c) is performed in the
presence of an oxidation catalyst.
8. The process of claim 7 wherein the oxidation catalyst comprises
a transition metal zeolite.
9. The process of claim 8 wherein the oxidation catalyst further
comprises a noble metal.
10. The process of claim 9 wherein the noble metal is supported on
the transition metal zeolite.
11. The process of claim 10 wherein the transition metal zeolite is
a titanium zeolite.
12. The process of claim 9 wherein the noble metal is supported on
a carrier.
13. The process of claim 12 wherein the carrier is selected from
the group consisting of carbon, titania, zirconia, niobia, silica,
alumina, silica-alumina, titania-silica, zirconia-silica,
niobia-silica, ion-exchange resins, and mixtures thereof.
14. The process of claim 12 wherein the noble metal is selected
from the group consisting of palladium, platinum, gold, rhenium,
silver, and mixtures thereof.
15. The process of claim 12 wherein the transition metal zeolite is
a titanium zeolite.
16. The process of claim 7 wherein step (c) is performed in the
presence of an oxidizing reagent.
17. The process of claim 16 wherein the oxidizing reagent comprises
oxygen.
18. The process of claim 16 wherein the oxidizing reagent comprises
hydrogen peroxide.
19. The process of claim 7 wherein step (c) is performed in the
presence of an acid.
20. The process of claim 19 wherein the acid is selected from the
group consisting of hydrobromic acid, hydrochloric acid, phosphoric
acid, nitric acid, sulfuric acid, carbonic acid, formic acid,
acetic acid, propionic acid, and mixtures thereof.
21. The process of claim 1 wherein the olefin is propylene and the
alkane is propane.
22. The process of claim 21 wherein the propane is separated from
propylene by distillation.
23. The process of claim 21 wherein the oxygenated product is
isopropanol, acetone, or a mixture of them.
Description
FIELD OF THE INVENTION
The invention relates to a process for oxidizing an olefin with
hydrogen and oxygen.
BACKGROUND OF THE INVENTION
Many different methods for the preparation of epoxides have been
developed. Commercially, propylene oxide is produced by the
chlorohydrin process or hydroperoxidation (see, e.g., U.S. Pat.
Nos. 3,351,635 and 4,367,342; EP 0 345 856). Unfortunately, both
processes have disadvantages. The chlorohydrin process suffers from
the production of a dilute salt stream. The hydroperoxidation
process, in which propylene is oxidized with an organic
hydroperoxide such as ethylbenzene hydroperoxide or tert-butyl
hydroperoxide, produces organic co-products such as t-butyl alcohol
or styrene, whose value must be captured in the market place.
Ethylene oxide is commercially produced by the direct oxidation of
ethylene with oxygen over a silver catalyst. Unfortunately, efforts
to epoxidize higher olefins (olefins containing three or more
carbons) such as propylene with oxygen in the presence of a silver
catalyst have failed to produce a commercial process (see, e.g.,
U.S. Pat. Nos. 5,856,534, 5,780,657 and 4,994,589).
Recent efforts have focused on the direct epoxidation of higher
olefins with oxygen and hydrogen. For example, the reaction may be
performed in the presence of a catalyst comprising gold and a
titanium-containing support (see, e.g., U.S. Pat. Nos. 5,623,090,
6,362,349, and 6,646,142), or a catalyst containing palladium and a
titanium zeolite (see, e.g., JP 4-352771).
Mixed catalyst systems for olefin epoxidation with hydrogen and
oxygen have also been disclosed. For example, Example 13 of JP
4-352771 describes the use of a mixture of titanosilicate and
Pd-on-carbon for propylene epoxidation. U.S. Pat. No. 6,008,388
describes a catalyst comprising a noble metal and a titanium or
vanadium zeolite, but additionally teaches that the Pd can be
incorporated into a support before mixing with the zeolite. The
catalyst supports disclosed include silica, alumina, and activated
carbon. U.S. Pat. No. 6,498,259 discloses the epoxidation of an
olefin with hydrogen and oxygen in a solvent containing a buffer in
the presence of a catalyst mixture containing a titanium zeolite
and a noble metal catalyst.
Unfortunately, undesirable reactions also occur in these
epoxidation processes. For example, the olefin can be hydrogenated
to the corresponding alkane (U.S. Pat. No. 6,867,312). It would be
desirable to convert the alkane formed from the epoxidation process
to more valuable oxygenated products.
SUMMARY OF THE INVENTION
This invention is a process comprising reacting an olefin,
hydrogen, and oxygen in the presence of an epoxidation catalyst
comprising a transition metal zeolite and a noble metal to produce
a product stream comprising an epoxide and an alkane. The process
also comprises separating the alkane from the product stream and
oxidizing it to produce at least one oxygenated product.
DETAILED DESCRIPTION OF THE INVENTION
The process of the invention include an epoxidation step. The
epoxidation step comprises reacting an olefin, hydrogen, and oxygen
in a reactor in the presence of an epoxidation catalyst comprising
a transition metal zeolite and a noble metal to produce a product
stream comprising an epoxide and an alkane. Zeolites generally
contain one or more of Si, Ge, Al, B, P, or the like, in addition
to oxygen. A transition metal zeolite (e.g., titanium zeolite,
vanadium zeolite) is a crystalline material having a porous
molecular sieve structure and containing a transition metal. A
transition metal is a Group 3-12 element. The first row of them
includes elements from Sc to Zn. Preferred transition metals are
Ti, V, Mn, Fe, Co, Cr, Zr, Nb, Mo, and W. Particularly preferred
are Ti, V, Mo, and W. Most preferred is Ti. The type of transition
metal zeolite employed depends upon a number of factors, including
the size and shape of the olefin to be epoxidized. For example, it
is especially advantageous to use titanium silicalite-1 (TS-1, a
titanium silicalite having an MFI topology analogous to that of the
ZSM-5 aluminosilicate) for the epoxidation of propylene. For a
bulky olefin such as cyclohexene, larger pore zeolites may be
preferred.
Suitable titanium zeolites include titanium silicates
(titanosilicates). Preferably, they contain no element other than
titanium, silicon, and oxygen in the lattice framework (see R.
Szostak, "Non-aluminosilicate Molecular Sieves," in Molecular
Sieves: Principles of Synthesis and Identification, (1989), Van
Nostrand Reinhold, pp. 205-282). Small amounts of impurities, e.g.,
boron, iron, aluminum, phosphorous, copper, and the like, and
mixtures thereof, may be present in the lattice. The amount of
impurities is preferably less than 0.5 weight percent (wt. %), more
preferably less than 0.1 wt. %. Preferred titanium silicates will
generally have a composition corresponding to the following
empirical formula: xTiO.sub.2.(1-x)SiO.sub.2, where x is between
0.0001 and 0.5000. More preferably, the value of x is from 0.01 to
0.125. The molar ratio of Si:Ti in the lattice framework of the
zeolite is advantageously from 9.5:1 to 99:1 (most preferably from
9.5:1 to 60:1). The use of relatively titanium-rich zeolites may
also be desirable. Particularly preferred titanium zeolites include
the class of molecular sieves commonly known as titanium
silicalites (see Catal. Rev.-Sci. Eng. 39(3) (1997) 209). Examples
of these include TS-1, TS-2 (having an MEL topology analogous to
that of the ZSM-11 aluminosilicate), and TS-3 (as described in
Belgian Pat. No. 1,001,038). Titanium zeolites having framework
structures isomorphous to zeolite beta, mordenite, and ZSM-12 are
also suitable for use.
The epoxidation catalyst also comprises a noble metal. Suitable
noble metals include gold, silver, platinum, palladium, iridium,
ruthenium, osmium, rhenium, rhodium, and mixtures thereof.
Preferred noble metals are Pd, Pt, Au, Re, Ag, and mixtures
thereof. While any of the noble metals can be utilized, either
alone or in combination, palladium and gold are particularly
desirable. Typically, the amount of noble metal present in the
catalyst will be in the range of from 0.01 to 20 wt. %, preferably
0.1 to 5 wt. %.
The noble metal and the transition metal zeolite may be on a single
particle or on separate ones. For example, the noble metal may be
supported on the transition metal zeolite. Alternatively, the
epoxidation catalyst comprises a mixture of a transition metal
zeolite and a noble metal, wherein the noble metal may be
essentially elemental (e.g., colloidal Pd), or it may be supported
on a carrier. Suitable carriers for the supported noble metal
include carbon, titania, zirconia, niobia, silica, alumina,
silica-alumina, titania-silica, zirconia-silica, niobia-silica,
ion-exchange resins, and the like, and mixtures thereof.
The manner in which the noble metal is incorporated in the
epoxidation catalyst is not critical. For example, the noble metal
may be supported on the transition metal zeolite or other carriers
by impregnation, ion exchange, adsorption, precipitation, or the
like.
There are no particular restrictions regarding the choice of the
noble metal compound or complex used as the source of the noble
metal. Suitable compounds include nitrates, sulfates, halides
(e.g., chlorides, bromides), carboxylates (e.g., acetate), and
amine or phosphine complexes of noble metals (e.g., palladium(II)
tetraammine bromide, tetrakis(triphenylphosphine)palladium(0)).
Similarly, the oxidation state of the noble metal is not critical.
Palladium, for instance, may be in an oxidation state anywhere from
0 to +4 or any combination of such oxidation states. To achieve the
desired oxidation state or combination of oxidation states, the
noble metal compound after being introduced into the epoxidation
catalyst may be fully or partially pre-reduced. Satisfactory
catalytic performance can, however, be attained without any
pre-reduction.
The weight ratio of the transition metal zeolite:noble metal is not
particularly critical. However, a transition metal zeolite:noble
metal weight ratio of 0.01-100 (grams of transition metal zeolite
per gram of noble metal) is preferred.
The epoxidation catalyst is preferably in the form of a suspension
or fixed-bed. The epoxidation step may be performed in a continuous
flow, semi-batch, or batch mode. It is advantageous to work at a
pressure of 1-200 bars. The epoxidation step is carried out at a
temperature effective to achieve the desired olefin epoxidation,
preferably at temperatures in the range of 0-200.degree. C., more
preferably, 20-150.degree. C. Preferably, at least a portion of the
reaction mixture is a liquid under the reaction conditions.
An olefin is required in the epoxidation step. Suitable olefins
include any olefin having at least one carbon-carbon double bond,
and generally from 2 to 60 carbon atoms. Preferably, the olefin is
an acyclic alkene of from 2 to 30 carbon atoms. The process of the
invention is particularly suitable for epoxidizing C.sub.2-C.sub.6
olefins. More than one double bond may be present in the olefin
molecule, as in a diene or triene. The olefin may be a hydrocarbon
or it may contain functional groups such as halide, carboxyl,
hydroxyl, ether, carbonyl, cyano, nitro groups, or the like. The
process of the invention is especially useful for converting
propylene to propylene oxide.
Oxygen and hydrogen are also required. Although any sources of
oxygen and hydrogen are suitable, molecular oxygen and molecular
hydrogen are preferred. The molar ratio of hydrogen to oxygen can
usually be varied in the range of H.sub.2:O.sub.2=1:100 to 5:1 and
is especially favorable at 1:5 to 2:1. The molar ratio of oxygen to
olefin is usually 1:1 to 1:20, and preferably 1:1.5 to 1:10.
Relatively high oxygen to olefin molar ratios (e.g., 1:1 to 1:3)
may be advantageous for certain olefins.
In addition to the olefin, oxygen, and hydrogen, an inert gas is
preferably used in the epoxidation step. Any desired inert gas can
be used. Suitable inert gases include nitrogen, helium, argon, and
carbon dioxide. Saturated hydrocarbons with 1-8, especially 1-6,
and preferably 1-4 carbon atoms, e.g., methane, ethane, propane,
and n-butane, are also suitable. Nitrogen and saturated
C.sub.1-C.sub.4 hydrocarbons are preferred inert gases. Mixtures of
inert gases can also be used. The molar ratio of olefin to gas is
usually in the range of 100:1 to 1:10 and especially 20:1 to
1:10.
The amount of transition metal zeolite used may be determined on
the basis of the molar ratio of the transition metal contained in
the transition metal zeolite to the olefin that is supplied per
unit time. Typically, sufficient transition metal zeolite is
present to provide a transition metal/olefin per hour molar feed
ratio of from 0.0001 to 0.1.
The epoxidation step preferably uses a solvent. Suitable solvents
are liquid under the reaction conditions. They include, for
example, oxygen-containing hydrocarbons such as alcohols, aromatic
and aliphatic solvents such as toluene and hexane, chlorinated
aromatic and aliphatic solvents such as chlorobenzene and methylene
chloride, nitriles such as acetonitrile, carbon dioxide, and water.
Suitable oxygenated solvents include alcohols, ethers, esters,
ketones, carbon dioxide, water, and the like, and mixtures thereof.
Preferred oxygenated solvents include water and lower aliphatic
C.sub.1-C.sub.4 alcohols such as methanol, ethanol, isopropanol,
tert-butanol, and mixtures thereof. Fluorinated alcohols can be
used.
It may be advantageous to use a buffer. The buffer is employed in
the reaction to inhibit the formation of glycols or glycol ethers
during the epoxidation, and it can improve the reaction rate and
selectivities. The buffer is typically added to the solvent to form
a buffer solution, or the solvent and the buffer are added
separately. Useful buffers include any suitable salts of oxyacids,
the nature and proportions of which in the mixture are such that
the pH of their solutions preferably ranges from 3 to 12, more
preferably from 4 to 10, and most preferably from 5 to 9. Suitable
salts of oxyacids contain an anion and a cation. The anion may
include phosphate, carbonate, bicarbonate, sulfate, carboxylates
(e.g., acetate), borate, hydroxide, silicate, aluminosilicate, or
the like. The cation may include ammonium, alkylammonium (e.g.,
tetraalkyl-ammoniums, pyridiniums), alkylphosphonium, alkali metal,
and alkaline earth metal ions, or the like. Examples include
NH.sub.4, NBu.sub.4, NMe.sub.4, Li, Na, K, Cs, Mg, and Ca cations.
The preferred buffer comprises an anion selected from the group
consisting of phosphate, carbonate, bicarbonate, sulfate,
hydroxide, and acetate; and a cation selected from the group
consisting of ammonium, alkylammonium, alkylphosphonium, alkali
metal, and alkaline earth metal ions. Buffers may preferably
contain a combination of more than one suitable salt. Typically,
the concentration of the buffer in the solvent is from 0.0001 M to
1 M, preferably from 0.0005 M to 0.3 M. The buffer may include
ammonium hydroxide which can be formed by adding ammonia gas to the
reaction system. For instance, one may use a pH=12-14 solution of
ammonium hydroxide to balance the pH of the reaction system. More
preferred buffers include alkali metal phosphates, ammonium
phosphate, and ammonium hydroxide.
The epoxidation step produces a product stream comprising an
epoxide and an alkane. The alkane is typically produced as a
byproduct from the hydrogenation of the olefin. For example, if
propylene is used as the olefin, propane may be formed in the
epoxidation step as a byproduct.
The process of the invention includes a step for separating the
alkane from the epoxidation product stream. For example, if
propylene is used as the olefin, the product stream may contain
propylene, propane, oxygen, hydrogen, inert gas (e.g., nitrogen),
solvent, and other byproducts. Readily condensable components
including propylene oxide, solvents (e.g., methanol, water), and
heavy byproducts (e.g., glycol, glycol ethers) can be separated
from the light materials comprised of propane, propylene, oxygen,
hydrogen, and inert gases by evaporation or distillation. The
mixture of propylene oxide, solvent, and heavy byproducts can be
distilled to isolate propylene oxide. Similar separations are
employed in other processes for making propylene oxide (see, e.g.,
U.S. Pat. Nos. 3,450,055, 3,464,897, 3,449,219, 3,580,819, and
5,973,171). The light materials (propane, propylene, oxygen,
hydrogen, and inert gases) can be separated into a C.sub.3 stream
(propylene and propane) and a lighter stream (oxygen, hydrogen, and
inert gases) (see U.S. Pat. No. 5,973,171). Propane and propylene
separation may be carried out by distillation, preferably at a
pressure of from 50 to 400 psig. More preferably, the distillation
is done at a pressure of from 250 to 350 psig. For other methods of
separating propane and propylene, see, Hydrocarbon Process., Int.
Ed. 66(4) (1987) 43; Chem. Eng. J. 84(3) (2001) 581; Ind. Eng.
Chem. Res. 34(12) (1995) 4413; WO 2003/093202; WO 2005/042449.
Propane separated from the product steam may contain small amount
of propylene (e.g., less than 5 wt. %, more preferably less than 1
wt. %, and most preferably less than 0.1 wt. %).
The separation of other alkanes from the corresponding olefins may
be accomplished similarly. In the epoxidation of 1-butene, for
example, a mixture of 1-butene and n-butane is obtained. n-Butane
may be separated from 1-butene by distillation (see, e.g., U.S.
Pat. No. 2,911,452).
The process of the invention also includes an oxidation step. This
step comprises oxidizing the alkane to at least one oxygenated
product. Oxidation of alkanes is well known in the art (see J. Mol.
Catal. A: Chem. 220 (1) (2004) 27; F. Canani and F Trifiro, "The
Multifunctional Properties of Heterogeneous Catalysts, Active and
Selective in the Oxidation of Light Paraffins," in Studies in
Surface Science and Catalysis 110: 3.sup.rd World Congress on
Oxidation Catalysis, R. K. Grasseli, et al., Elsevier Science B.V.
(1997) pp. 19-34).
Generally, the oxidation of an alkane occurs in the presence of an
oxidizing reagent. Suitable oxidizing reagents include oxygen,
hydrogen peroxide, organic hydroperoxides (e.g., tert-butyl
hydroperoxide, ethylbenzene hydroperoxide, cumene hydroperoxide),
peroxy acids (e.g., peroxyacetic acid), ozone, and the like. Due to
its low cost, oxygen is a preferred oxidizing reagent. In
particular, air may be used as the source of oxygen. Another
preferred oxidizing reagent is hydrogen peroxide because its only
byproduct is water.
Oxidation of alkanes can give a variety of oxygenated products,
including alcohols (see, e.g., U.S. Pat. Nos. 4,918,238, 4,978,799,
5,235,111, 5,345,010, 5,354,857, 5,409,876, and 5,663,328),
aldehydes (see, e.g., J. Catal., 202(2) (2001) 308; Appl. Catal., A
217(1-2) (2001) 111; U.S. Pat. No. 4,859,798), ketones (e.g., Appl.
Catal., A 217(1-2) (2001) 111; EP 0126488; U.S. Pat. Nos.
4,038,322, 5,235,111, and 5,409,876), carboxylic acids and
anhydrides (see, e.g., U.S. Pat. Nos. 5,543,532, 5,663,328,
6,646,158, 6,919,295, and 6,914,029). Oxidation of propylene may
produce isopropanol, acetone, propionaldehyde, acrolein, acrylic
acid, propionic acid, and the like, and mixtures thereof. Under
appropriate reaction conditions, oxidation of propane may give
isopropanol, acetone, or a mixture of them. Oxidation of n-butane
may produce 1-butanol, 2-butanol, methyl ethyl ketone,
n-butylaldehyde, n-butyric acid, maleic acid, maleic anhydride, and
the like, and mixtures thereof.
The oxidation of an alkane is preferably performed in the presence
of an oxidation catalyst. An oxidation catalyst is any material
that is capable of catalyzing the oxidation of an alkane. The
oxidation catalyst typically comprises a transition metal. Suitable
transition metals include elements in Groups 3 to 11. The first row
of these metals includes Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu. The
transition metal may be present in any suitable oxidation state as
long as it is capable of catalyzing the reaction. Examples of
suitable oxidation catalysts are: supported transition metals (see,
e.g., U.S. Pat. Nos. 5,235,111, 5,409,876, and 5,623,090),
transition metal salts (see, e.g., EP 0126488; U.S. Pat. Nos.
4,038,322 and 5,543,532), transition metal complexes (see, e.g.,
U.S. Pat. Nos. 4,918,238, 4,978,799, 5,354,857, and 5,663,328),
transition metal oxides or supported transition metal oxides (see,
e.g., U.S. Pat. No. 5,345,010), mixed metal oxides (see, e.g., U.S.
Pat. Nos. 6,646,158 and 6,919,295), transition metal zeolites (see,
e.g., J. Catal. 202 (2) (2001) 308; Stud. Surf. Sci. Catal., 97
(1995) 367; Sci. Tech. Catal. (1994) 31; U.S. Pat. No. 5,126,491),
heteropolyacids or polyoxometallates (see, e.g., Appl. Catal., A
217(1-2), (2001), 111; Pure Appl. Chem. 72(7) (2000) 1289; U.S.
Pat. Nos. 4,859,798, 5,334,780, and 6,914,029), and mixtures
thereof. The oxidation catalyst may be soluble, partially soluble,
or essentially insoluble in the reaction mixture under the reaction
conditions.
Preferably, the oxidation catalyst comprises a transition metal
zeolite. Suitable transition metal zeolites for the epoxidation
catalyst described above are applicable for the present oxidation
catalyst.
In one particular example, the oxidation catalyst comprises a noble
metal and a transition metal zeolite, wherein the oxidizing reagent
comprises oxygen and hydrogen (see, e.g., J. Chem. Soc., Chem.
Comm. (1992) 1446; Sci. Tech. Catal. (1994) 31). Suitable noble
metals and transition metal zeolites for the epoxidation catalyst
and its preparation methods described above are applicable for the
present oxidation catalyst.
The oxidation catalyst is preferably in the form of a suspension or
fixed-bed. The oxidation step may be performed in a continuous
flow, semi-batch, or batch mode. It is advantageous to work at a
pressure of 1-200 bars. The oxidation step according to the
invention is carried out at a temperature effective to achieve the
desired alkane oxidation, preferably at temperatures in the range
of 0-200.degree. C., more preferably, 20-150.degree. C.
The oxidation step may use a solvent. Suitable solvents are liquid
under the reaction conditions. They include, for example,
oxygen-containing hydrocarbons such as alcohols, aromatic and
aliphatic solvents such as toluene and hexane, chlorinated aromatic
and aliphatic solvents such as chlorobenzene and methylene
chloride, nitriles such as acetonitrile, carbon dioxide, and water.
Suitable oxygenated solvents include alcohols, ethers, esters,
ketones, carbon dioxide, water, and the like, and mixtures thereof.
Preferred oxygenated solvents include water and lower aliphatic
C.sub.1-C.sub.4 alcohols such as methanol, ethanol, isopropanol,
tert-butanol, and mixtures thereof. Fluorinated alcohols can be
used.
The oxidation step is preferably carried out in the presence of an
acid. An acid is used to improve the rate or the selectivity of the
oxidation reaction. Suitable acids include hydrobromic acid,
hydrochloric acid, phosphoric acid, nitric acid, sulfuric acid,
carbonic acid, carboxylic acids (e.g., formic acid, acetic acid,
propionic acid), and the like, and mixtures thereof.
Following examples merely illustrate the invention. Those skilled
in the art will recognize many variations that are within the
spirit of the invention and scope of the claims.
EXAMPLE 1
Pd/TS-1 Catalyst
A TS-1 sample prepared by following procedures disclosed in U.S.
Pat. Nos. 4,410,501 and 4,833,260 is calcined at 550.degree. C. in
air. It contains 2.1 wt. % Ti and <0.1 wt. % C.
Spray dried TS-1 (80 wt. % TS-1 and 20 wt. % silica binder,
particle size=35 micron, 12 g) is slurried in deionized water (24
g) and the pH is adjusted from 4.8 to 7.3 with 5 wt. % aqueous
ammonium hydroxide. After mixing for 5 min, an aqueous tetraammine
palladium dinitrate solution (containing 0.97 wt. % Pd, 1.22 g) is
added with mixing over 1 min. The pH is then adjusted from 6.1 to
7.3 with 5 wt. % aqueous ammonium hydroxide and the slurry is
agitated at 30.degree. C. for 10 min. The pH is adjusted from 6.7
to 7.3 and agitated at 30.degree. C. for 20 min. The pH is adjusted
from 7.0 to 7.3 with 5 wt. % aqueous ammonium hydroxide. The slurry
is filtered and the filter cake is washed three times by
reslurrying it in deionized water (25 g) followed by filtration.
The solids are then air dried overnight and dried in a vacuum oven
at 50.degree. C. for 6 h. The dried solids contain 0.1 wt. % Pd and
2.1 wt. % Ti.
The above material is calcined in air in an oven that is heated
from 23 to 110.degree. C. at a rate of 10.degree. C./min and
maintained at 110.degree. C. for 2 h, then heated to 300.degree. C.
at a rate of 2.degree. C./min and maintained at 300.degree. C. for
4 h. The calcined solids (containing 0.1 wt. % Pd, 2.1 wt. % Ti,
<0.1 wt. % C, <0.1 wt. % N, and <0.1 wt. % H) are
transferred to a quartz tube, heated to 100.degree. C. and treated
with 5 vol. % hydrogen in nitrogen (flow rate, 100 mL/min) for 4 h.
After the hydrogen treatment, nitrogen is passed through the solid
for 1 h before it is cooled to 23.degree. C. The Pd/TS-1 (Catalyst
A) is recovered.
EXAMPLE 2
Epoxidation of Propylene
An ammonium phosphate buffer solution (0.1 M, pH 6) is prepared as
follows. Ammonium dihydrogen phosphate (11.5 g) is dissolved in
deionized water (900 g). Aqueous ammonium hydroxide (30 wt. %
NH.sub.4OH) is added to the solution until the pH reads 6 via a pH
meter. The volume of the solution is then increased to exactly 1000
mL with additional deionized water.
A 300-mL stainless steel reactor is charged with Catalyst A (0.7
g), the buffer solution prepared above (13 g), and methanol (100
g). The reactor is then charged to 300 psig with a feed gas
consisting of 2 volume percent (vol. %) hydrogen, 4 vol. % oxygen,
5 vol. % propylene, 0.5 vol. % methane, and the balance nitrogen.
The pressure in the reactor is maintained at 300 psig via a back
pressure regulator with the feed gases passed continuously through
the reactor at 1600 mL/min (measured at 23.degree. C. and 1
atmosphere pressure). In order to maintain a constant solvent level
in the reactor during the run, the oxygen, nitrogen and propylene
feeds are passed through a 2-L stainless steel vessel (saturator)
preceding the reactor containing 1.5 L of methanol. The reaction
mixture is heated to 60.degree. C. while it is stirred at 1500 rpm.
The gaseous effluent is analyzed by an online gas chromatograph
(GC) every hour and the liquid analyzed by offline GC at the end of
the 18 h run. The products formed include propylene oxide (PO),
propane, and derivatives of propylene oxide such as propylene
glycol, propylene glycol monomethyl ethers, dipropylene glycol, and
dipropylene glycol methyl ethers. The catalyst productivity is 0.37
g POE/g cat/h. Propylene to POE selectivity is 68%. Propylene to
propane selectivity is 32%. The catalyst productivity is defined as
the grams of PO formed (including PO which is subsequently reacted
to form PO derivatives) per gram of catalysts (Pd/TS-1) per hour.
POE (mole)=moles of PO+moles of PO units in the PO derivatives.
PO/POE=(moles of PO)/(moles of POE).times.100. Propylene to POE
selectivity=(moles of POE)/(moles of propane formed+moles of
POE).times.100. Propylene to propane selectivity=(moles of propane
formed)/(moles of propane formed+moles of POE).times.100.
EXAMPLE 3
Oxidation of Propane
A 100-mL Parr reactor equipped with a magnetic stirring bar is
charged with Catalyst A (0.2 g), methanol (18 g), and deionized
water (2 g). After the reactor is closed, propane (6 g) is added.
The reactor is pressurized to 210 psig with hydrogen and to 1300
psig with a gas mixture containing 4% oxygen in nitrogen. The
reactor is heated to 80.degree. C. and kept at 80.degree. C. for 2
h. The reaction mixture is cooled to 23.degree. C. and analyzed by
GC. It contains 0.028 wt. % isopropanol.
EXAMPLE 4
Oxidation of Propane in the Presence of HBr
The procedure of Example 3 is repeated except that an aqueous HBr
solution (0.055 wt. %, 0.22 g) is also charged in the reactor. GC
analysis shows that the mixture contains 0.16 wt. % isopropanol and
0.02 wt. % acetone at the end of the reaction.
EXAMPLE 5
Oxidation of Propane in the Presence of HBr and H.sub.3PO.sub.4
The procedure of Example 3 is repeated except that deionized water
(1.5 g), an aqueous HBr solution (0.055 wt. %, 0.22 g), and an
aqueous H.sub.3PO.sub.4 solution (85 wt. %, 0.52 g) are charged in
the place of deionized water (2 g). GC analysis shows the mixture
contains 0.09 wt. % isopropanol and 0.31 wt. % acetone at the end
of the reaction.
EXAMPLE 6
Oxidation of Propane in the Presence of Oxo-TEMPO
The procedure of Example 3 is repeated except that an aqueous
4-oxo-TEMPO (4-oxo-2,2,6,6-tetramethyl-1-piperidinyloxy radical)
solution (0.1 wt. %, 0.3 g) is also charged in the reactor. GC
analyses show the mixture contains 0.08 wt. % isopropanol and 0.008
wt. % acetone at the end of the reaction.
Repeating the procedures of Examples 3-6 using propane isolated
from the product stream of Example 2 shall provide similar
results.
EXAMPLE 7
Pd/Nb.sub.2O.sub.5 Catalyst
Pd(NH.sub.3).sub.4Br.sub.2 (0.8 g) is dissolved in deionized water
(120 g) in a beaker. In a separate beaker, niobium oxide powder
(obtained from Reference Metals, 25 g) is slurried in deionized
water (80 g). The palladium salt solution is added to the niobium
oxide while it is being stirred over a period of 10 min. The slurry
is stirred at 23.degree. C. for another 2 h. The solid material is
separated by centrifugation and washed by reslurrying it in
deionized water (80 g). The centrifugation and washing step is
repeated 4 times. The solid material is dried in a vacuum oven at 1
torr at 50.degree. C. The dried solid thus obtained contains 1.2
wt. % Pd, 1.6 wt. % Br, 67 wt. % Nb, and 0.4 wt. % N.
The dried solid is calcined in air by heating it from 23 to
110.degree. C. at a rate of 10.degree. C./min and maintaining the
temperature at 110.degree. C. for 2 h, then heating to 350.degree.
C. at a rate of 2.degree. C./min and maintaining the temperature at
350.degree. C. for 4 h. The calcined solid (Catalyst B) contains
1.1 wt. % Pd, 0.51 wt. % Br, 67 wt. % Nb, and <0.1 wt. % N.
EXAMPLE 8
Oxidation of Propane with Catalyst Mixture
A 100-mL Parr reactor equipped with a magnetic stir bar is charged
with Catalyst B (0.1 g), TS-1 powder (2 wt % Ti, 0.2 g), methanol
(18 g), and deionized water (2 g). After the reactor is closed,
propane (6 g) is added. The reactor is pressurized to 210 psig with
hydrogen and to 1300 psig with a gas mixture containing 4% oxygen
in nitrogen. The reactor is heated to 80.degree. C. and kept at
80.degree. C. for 2 h. The reaction mixture is cooled to 23.degree.
C. and analyzed by GC. It contains 0.19 wt. % acetone and 0.02 wt.
% isopropanol.
EXAMPLE 9
Oxidation of Propane with Catalyst Mixture in the Presence of HBr
and H.sub.3PO.sub.4
The procedure of Example 8 is repeated except that deionized water
(1.5 g), an aqueous HBr solution (0.055 wt. %, 0.22 g), and an
aqueous H.sub.3PO.sub.4 solution (85 wt. %, 0.52 g) are charged in
the place of 2 g of deionized water. GC analysis shows that the
mixture contains 0.4 wt. % acetone and 0.044 wt. % isopropanol.
EXAMPLE 10
Oxidation of Propane with Hydrogen Peroxide
A 100-mL Parr reactor equipped with a magnetic stirring bar is
charged with TS-1 (Ti=2.3 wt. %, 0.2 g), methanol (20 g), and
aqueous hydrogen peroxide (30 wt. %, 0.4 g). The reactor is closed
and purged with nitrogen. Propane (6 g) is added and the reactor is
pressurized to 600 psig with nitrogen. The reactor is heated to
60.degree. C. and allowed to react for 1.75 h. The reaction mixture
is cooled to 23.degree. C. and analyzed by GC. GC analysis shows
that the mixture contains 0.36 wt. % isopropanol and 0.1 wt. %
acetone.
* * * * *